Oscillator controlled relay circuit



March 25, 1952,v R. T. scHENcK OSCILLATOR CONTROLLED RELAY CIRCUIT 4 Sheets-Sheet 1 Filed Dec. 1l, 1945 -mbm March 25, 1952 Filed Dec. 11, 1945 FIEE.

R. T. SCHENCK OSCILLATOR CONTROLLED RELAY CIRCUIT 4 Sheets-Sheet 2 ,gui am.

March 25, 1952 R. T. scHENcK 2,590,825

OSCILLATOR CONTROLLED RELAY CIRCUIT Filed Dec. 11 1945 4 Sheets-Sheet 5 March 25, 1952 R. T. scHENcK oscILLAToR CONTROLLED RELAY CIRCUIT 4 Sheets-Sheet 4 Filed DeC- ll, 1945 Patented Mar. 25, 1952 1r-UNITED s'rlii'ras PATENT OFFICE osoiLLAroRv coNTRoLLEn RELAY cmourr Remsen T. Schenck, Lower Mount Bethel Township, Northampton County, Pa., assigner to the United States of America as represented by the United States Atomic Energy Commission Application December 11, 1945, serial No. 634,314 e claim. (c1. 17a-32o) This invention relates to an electronic control system particularlyl designed for use in 'connectionk with liquid level or liquid density control or indicating apparatus. j

In various chemical procedures, it is necessary to control very accurately the level or density of a reacting liquid, or liquids. For example, Where a reaction takes place at the interface of two mutually reactive solutions, it may be necessary t maintain 'the interface level or solution densities within very close limits. When the reacting liquids involved in this or other procedures requiring liquid level or density control are' of a radioactive or of an otherwise inherently dangerous character, the provision of satisfactory control apparatus for regulating liquid or interface levels and for controlling density has proven a most troublesome one, and the apparatus heretofore available in the art has been, in general, unsatisfactory.

YSome of the more serious deficiencies in the prior art apparatus result from the fact that the operation of such apparatus requires either mechanical or' electrical contact with the liquid or liquids to be regulated, or requires that a beam of light shallbepassed through a sample of such liquid or liquids. In the case of radioactive liquids, physical contact between the liquid and the regulating apparatus is usually either impractical or undesirable, and the light beam type apparatus is equally unsatisfactory due to the impossibility of maintaining uniform light transmission characteristics in known transparent materials in the presence of intenseradioactive emanations. Y

The Yprincipal. object of the present invention, therefore, isto provide liquid level or liquid density control apparatus which shall 'be operable without requiring any mechanical or electrical contact between the control apparatus and the material whose level or density is being controlled, andwhich shall be unaffected by exposure to radioactive emanations. As will hereinafter appear, this Iobject is accomplished by the provision of an electronic control system which includes a tuned oscillator and an amplis fyingsystem, so arranged that the oscillator is at all VtimesY under the control of a float which is disposed'within the liquid whose level or density'is to Vbe controlled and which is inductively associated with the electronic system. This arrangement makes possible a control system which is completely free from the diiiiculties and undesirable features of the prior art apparatus.

The principles ofthe invention will-be made apparent in the following description and the accompanying'drawings of one satisfactory'em# bodiment thereof, wherein:

Fig. 1 is a circuit diagram of an electronic control systemmade and operated in accordance with the invention;

Fig. 2 is a side elevational view partially in section of a float and oscillatorcoil unit particularly designed for controlling the level of the liquid interface between two bodies of reacting liquid;

Fig. 3 is a sectional-view of the apparatus of Fig. 2 taken on the line 3-3 of Fig. 2;

Fig. 4 is a sectional View of apparatus for use in density control showing a float andv oscillator coil unit; and

Fig. 5 is a sectional view of the apparatus'of Fig. 4 on the line 5-5 of Fig. 4.

The electronic control system of the present invention employs a vacuum tube oscillator unit which is so designed that it operates at peak output when a liquid level or liquid density float of special design is disposed in a xed position relative to a portion of the oscillator circuit. Preferably, an L-Cl type oscillator is used, this circuit permitting the use of a float which includes means of magnetic material disposed for move ment within the frequencycontrolling coil of the oscillator. Movement of this float in response to density or liquid level changes will alter the ingductance of the `oscillator circuit and will radically alter the fundamental or normal frequency of the oscillator output. The oscillator output is amplied by a sharply tuned amplier which passes thenormal oscillator outputbily,V and by the use 'of suitable `electronic units is arranged tore'nergizethe operating coil ofafcontrol relay. When the'V float is at the predetermined level the liquid, the oscillator output is at the fundamental or normal frequency and maximum power is passed by the ampliiier` circuit. Thevrelay coil isv decnergized and the control relay rests inthe inactive position. 4When the liquid level changes the constants of the oscillator tanlgcirf cuit are altered, and the outputof the oscillator capableof being passedand amplified by the tuned amplifier portion `of' the circuit sharply decreases. Thisl energizes the relay coil and actuates the control relay. Suitable corrective mechanism is thereby putinto operation. I

While Yvarious electronic circuit arrangements may Vbe used to accomplish the operation de,- scribed above, a particularly satisfactory system utilizing a triode oscillator Il, a pentode ampli- Iier L3, a diode rectifier l5, and apentoderelay 3 l1, is illustrated in Fig. '1'. Oscillator tube l2 may comprise a simple triode such as a 6J5, the specific circuit constants given below being exemplary for use with such a tube. The oscillator tank circuit is provided by a grid lwinding Lg, which is inductively coupled to a plate winding L11, and a variable trimmer condenser C2 of about 280 micro-micro-farads capacity. One side of the tank circuit is connected to the grounded cathode I9 of the oscillator tube IZ and the other side is connected to the control grid 2l in a conventional manner. A 50,000 ohm resistance R1 is connected between the grid 2| and the cathode The plate winding Lp of the oscillator-circuit is connected at one side to the grid 2l and at the other side to the plate 23y through a blocking condenser C1 of about 100 micro-microfarads. The plate output passes through the primary winding 25 of an IF transformer 2l of conventional design tuned to a specific frequency,

such as 455-kilocycles, and is connected to a suitable negatively grounded source of positive plate potential of 300 volts through a resistance R2 of 10,000 ohms.y The potential side of the primary winding 25 of the IF transformer 2'1 is 'by-passed to ground by the condenser C3 which has a capacity of .1 micro-farad.

The grid winding Lg in the oscillator tank circuit is designed to producer oscillation at a frequency of 455 kilocycles when the magnetic float, in Fig. 1, is at a predetermined position Within the windings Lg and Lp. It will be understood that this frequency may be of any value and that the use of 455 kilocycles was dictated solely by the availability of commercial IF transformer equipment designed to operate at that frequency. Conveniently, the oscillator windings or coils Lg and Lp may be disposed so as to surround a tube of glass or other non-magnetic material containing the liquid or liquids 'whose level or Adensity is `to be controlled. Hence the actual dimensions of the oscillator windings Lg and Lp Lwill usually have to be determined by experiment. In one specific instance, where the windings were intended to be disposed about a 3A; in. iioat tube, the grid winding consisted of about '70 turns of No. 30, B & S, enameled wire, closely wound in two layers. The dimensions of the plate winding Lp are of course not critical, and in this instance it was found convenient to apply two additional layers o f wire on top of the grid winding Lp for this part of the unit. Additional details of exemplary coil and float structures will be described in subsequent paragraphs. The essential requirement is merely the provision of a coil and float structure so arranged that movement of the iioat alters the inductance of the oscillator tank circuit, and hence the frequency of the oscillator output.

One of the terminals of the secondary winding 29 of the input IF transformer 2l is connected to the control grid 3l of a pentode amplifier i3, which may be a 6SK'7, and the other side of the secondary winding 29 is connected to ground, as shown. The suppressor grid 33 of the 6SK7 is tied to the cathode 35, and the cathode 35 is conplied from a suitable negatively grounded source of positive potential of 300 volts through a resistor R5 of 10,000 ohms which is connected in series with the primary winding 4| of the output IF transformer d3. A decoupling condenser C5 of .1 micro-farad is connected across the resistor R5 and the grounded plate voltage source as shown. The output from secondary winding d5 of the IF output transformer 43 is rectified by means of the diode rectifier tube I6, which may comprise one of the sets of elements of a GHG, and the rectified output is fed to a load resistor Re of 100,000 ohms connected in series with the winding'll5 and the tube elements, as shown. A condenser C7 of .02 micro-farad is connected across the load resistance Re.

The output of the oscillator circuit as described has an amplitude of about 4 volts, and the rectied output of the amplifier produces a peak D. C. potential across the load resistance Re of about 25 volts. This potential is applied to the control grid di of the pentode amplifier relay tube. I8, which may comprise the pentode section of a GADZG, or it may comprise a simple pentode unit l such as a 6V6.

The suppressor grid i9 of the pentode Il is tied to the cathode 5l, as shown, and the screen 53 is similarly tied to the plate 55, the tube being of a type wherein the screen operates at the saine potential as the plate. The cathode 5I is grounded, and the plate 55 is connected to a 300 volt, negatively grounded, D. C. source through a platecurrent relay 5l and a current limiting resistor R10 of 10,000 ohms. VThe relay 5l is of the 4 pole, double throw type, and the contacts are held in the position shown when there is insufficient current flowing through the relay coil 59 to actuate the relay 5i', i. e., when the oscillator is delivering its maximum output to the rectifier. When the oscillator frequently changes and the amplieroutput drops off, the relay coil 59 is fully energized and the relay contacts move to the other position effecting the energization of suitable control circuits GI and 62 and a pilot light 63. Any suitable apparatus for effecting liquid level or density control may be operatively connected to the circuits 6I and 62.

The circuit arrangement, as described, is usually sufficient for effecting satisfactory control in instances where nothing more is desired than simple liquid level control or simple density control. In instances where it is necessary to control the interface level between reacting liquids, it is sometimes necessary to employ somewhat more sensitive control equipment, and in those instances, the alternative operation of a simple relay, such as the relay 51, is not suflicient to effect the desired control. For this reason, the system illustrated in Fig. 1 also includes a special circuit designed to effect the electronic operation of one or a series of valves, or other control mech anisms, formomentary periods only. This special circuit is also placed in operation when the relay 5'! is energized, since contacts 8l are opened also. This Valve operating circuit includes a gas triode E5, such as an 884, connected in a conventional relaxation oscillator circuit having a long time constant and so coupled to a power pentode 5l', which may be a GVG, that the pentode cathode 69 is held at a potential about 5 volts less positive than the plate supply voltage for the gas triode 55, while the control grid 'H of the pentode 51 is at the same potential as the plate i3 of the gas triode 55. To accomplish this, the cathode 'l5 of the triode 65 is connected to a source of negativepotentia'l of the order-fof about 24U-250;volts', relative: -to ground.' "The triode grid"11:isicon-v nected tota source of negative potential of. about 270 volts'V relative to ground through a resistor R'rof 50,000 ohms. The triode plate 13 is connected'to a'source of positive potential relative to ground'of about 5 volts in series'with a fixed resistor Re of 100,000 ohms and a variable resistor R9 of 3 megohms which resistors together comprise `the circuit charging resistance. The charging condenser Ca is of about 4 micro-farads capacity and is connected in a conventional manner from the plate 13 to the end of the grid resistor R7 connected to the negative potential source.

The cathode 69 of a power pentode 61 is connected to ground and the suppressor grid 19'is tied. thereto, asillustrated. The pentode plate 8|-and the screenvgrid 83 are tied together and are connected to a source ofpositive potential of about 300 volts through the operating coil84Y of a plate circuit relay 85 and a current limiting resistor R11 o'f 5000 ohms. The zero potential sideof the positive voltage source for this tube, similar to the other potential sources, is connected to ground.

The valve operating circuit operates in the following manner: When the relay 51 is energized as a result of a decrease in the output of the amplifier, the contacts B1 will 4be opened, and the high negative bias on the grid 1| that has cut off the plate current through vacuum tube v8| will be removed. At this instant the gas triode plate 13 and the control grid 1| of the power pentode 61 are at a potential which is negatively far below the triode plate supply voltage volts relative to. ground). The potential between plater 13 and grid 1| with respect to ground rises, thus charging condenser Ca. Since condenser CS ischarged through resistors Ra and R9, the time constant-of this RC circuit will determine the rate at which the potential of grid 1| rises with respect to ground. When the pentode grid bias has been suiiiciently reduced, the pentode 61 becomes conducting and the resultant plate current energizes the winding 84 of the plate circuit relay 85, which in turn moves the relay contacts to effect energization of the associated valves or other apparatus. Almost as soon as this state is reached, however, the triode 65 again fires, and the potential of its plate 13 drops rapidly toward thev potential of its cathode 15 thereby greatly increasing the negative potential applied to the control grid 1| of the pentode 61 to effect cut-01T of that tube. The relay coil 84 is denergized, the contacts of the relay 85 open, and the operation of the associated control valves or other apparatus is stopped. Operation of the control valves or other apparatus for an extremely short interval of time is thereby made possible. The frequency of repetition of the Valve operating cycle is determined by adjustment of the variable resistor R9, and the cathode bias for the triode S5 is selected to determine the plate potential relative to ground at which the tube res, and thereby controls the fractionof each cycle during whichthe pentode is conductive, i. e., the length of time the contacts of the relay 85 are closed. The length of the firing period can be varied from a fraction of a second to periods of time upwards of a minute, and the period of time the contacts of the relay 85 are held in the closed position can be varied from zero to several seconds. Of course, when the output of the amplier again approachesits maximum value, the relay 51 is desusceptible of use in connection withother cir-- cuit arrangements where momentary operation of controlled equipmentin response tothe operation of. standard. .type relays, or the like, is desired. n

Thestruc'turalvv features of two Vtypes Vof 'come bination oscillator coil andfloat assemblies, suitable for use in the system described above, are shown in the other figures of thek drawings. The

device shown in Figs. 2 and 3 is intended forause` in maintaining the level of a liquid vinterface .at a predetermined elevation. A portion'ofa clo. sure containing the two liquids isshown'at 9|.- The iioat unit 93 of this device is adapted to be contained within a tube of glass or other nonmagnetic material which is connected with the two liquids contained in the main closure 9| by suitable elbow connections 91 and 99. The float 93 is of conventional form and is provided with suitable protuberances |0| for preventing it from sticking to the inner surface of the tube 95 and with a skirt |03 sov arranged` that it will come to rest at the liquid interface. Thev oat is designed to have a speciiic gravity between the specic gravities of the'two liquids whose interface is to be maintained* The iioat. is` weighed by magnetic means which may comprisea number of rectangular shaped pieces |05 of-'silicon steel arranged in a rectangularlyshaped stack as illustrated.- About 5 grams of steel were used in connection with an apparatus oscillator using coil windings having the dimensions previously described. The oscillator coils Lp andLg are conveniently wound on a suitable insulatingspool |25 disposed about the oatrtube 95.. 1 Connections |09 provided between the ilo'at tube 95'and the elbow section 91 and 99 desirably include restrictions for preventing the iloat 93 fromleaving the 'oat tube. Since a rise in the. interface level between the liquids contained in the clo'` sure 9| will cause the oat 93 to displace a'volum'e of the heavier density liquid that is greater than its weight, the float 93 -will vveil'ecta"c'or"espond ing rise, and this will 'change the inductance of the oscillator coil circuit, thereby. initiating'the' operation of the interface level control, a's`described above.

The combination float and oscillator coil device illustrated in Figs. 4 and 5 is similar to the device just described except that the iioat is of the hydrometer type and has been designated by lnumeral |01, thus adapting this device particularly for density control. The float tube Hilf-is cylif drical and is provided with sl'lt'able'ilagecon-` nections I whereby it may be connected' to the body of liquid whose density or"levellit`1is1vde sired to regulate. Oscillator coils vLip andllg of suitable design are wound on an insulating spool ||3, which is disposed about oat tube Il!) ina fixed position. The hydrometer type oat |01 has a main body section ||5 of somewhat smaller cross section than the tube |l'0 and is provided with protuberances ||1 for preventing the float from sticking in the float tube I l0. The float also includes a conventional, cylindrical, upper section l i9 of reduced diameter, and the hydrometer weighting comprises a small bundle 12| of silicon steel sheets or other magnetic material disposed at the lower end thereof. It will be apparent that changes in the density of a liquid contained in the float tube H will cause the hydrometer to move upward or downward, thereby altering the position of the steel sheets l2! contained therein relative to the oscillator coils Lg and Lp. This will vary the inductance and hence the oscillation frequency of the oscillator circuit, as previously described.

It will be apparent that the circuit constants enumerated hereinbefore are merely exemplary of a typical set ci constants that will give satisfactory operation. it should be noted, however, that wide variations may be made in some of the constants. For example,

(c) C1 should merely be large enough to provide adequate excitation while still having an impedance large compared with that of primary 25. The value will depend on the design'of the oscillator coil.

(b) C2 should be of capacity and range suf cient to tune the oscillator circuit to the intermediate frequency. The value will depend on the design of the oscillator coil and on the distributed capacity of the connecting line.

(e) R1 may be from 20,000 to 100,000 ohms, or may be unnecessary.

(d) C3, Ci, Ce, Ce are ley-pass condensers and are very uncritical. Values from 0.1 to .25 mid. are equally suitable.

(e) R2, R4, and R5 are merely decoupling resistors and may range from 1,000 to 100,000 ohms with practically no diilerence in performance.

ff) R3 has an optimum value of 300 ohms, but may range from 200 to 500 ohms.

(g) Re and'Ci are to some extent interdependent. They may vary between 50,000 and 1 million ohms and between 100 mmfd. and .l mid.. but low capacity should be associated with high resistance and vice versa. 100,000 ohms is suitable for .0l-.02 mfd.

(h.) The values of Rm and R11 are determined by the characteristics of relays 51 and 85.

(j) Ra may lie between 30,000 and 500,000 ohms.

(7c) Ca and RB+R9 form a time controlling circuit. The values are determined by the time constant desired in the relaxation oscillator and cover a wide range.

(in.) The potential with which the screen grid 3l of pentode I3 is served is not critical, and may reasonably be anywhere between 50 and 150 volts positive.

While tubes I8 and 6l are illustrated as triode connected, it should be noted that where greater sensitivity is required these tubes may be connected, for example, as pentodes instead.

It should be further noted that while the density float is illustrated in the drawing at air interface in a sight tube, in some applications this would not respond fast enough to changes in density of the main body of the solution because of stagnation in the sight tube. An alternative arrangement is to completely submerge the float in the main tube carrying the circulating solution so as to respond instantly.

While, for the sake of simplicity, only one coil and one control circuit are illustrated as associated with the interface level, it would be possibl-e to adjust this to correct for an increase or a decrease in the interface level but not both at the same time. In order to hold an interface within predetermined limits against any tendency either to rise or to fall, it is necessary to provide two coils each with its associated control circuit regulating the appropriate correcting device and to position them so that the steel oat core lies between them when the interface is at the desired level.

It is also necessary to prevent the iloat from rising far enough to carry the core above the upper edge of the upper coil or from falling far enough to carry the core below the lower edge of the lower coil. Suitable stops (not shown) may be provided for this purpose along the inner surface of tube 95.

In the foregoing, there has been disclosed the features of an improved liquid level or liquid density control system. The system is operable without requiring any actual contact between the apparatus resting -upon the liquid whose level or density is to be controlled and the remainder of the control mechanism which may be exterior to the liquid container. The disclosed system is accurate and reliable in operation, and it obviates all of the disadvantages of the prior art devices. The features of the invention which are believed to be new are expressly set forth in the appended claims.

What is claimed is:

l. An electrical control circuit which is operable to effect the repetitive energica-tion of equipment associated therewith for very short intervals of time comprising a vacuum tube saw-tooth sweep circuit, a relay control tube having a cathode, a plate and a control grid coupled to said sweep circuit, and a relay connected for energization by said relay control tube, the cathode of said relay control tube being maintained at a voltage which is only slightly less positive than the plate supply for the sweep circuit tube, the control grid of the relay control tube being iaintained at the same potential as the plate of the sweep circuit tube, and the cathode of the sweep circuit tube being maintained at a substantial negative potential relative to the potential of the cathode of the relay control tube.

2. An electrical control circuit which is operable to eiiect the repetitive energiaation of equip ment associated therewith for very short intervals of time comprising a gas filled triode connected in a saw-tooth sweep circuit, a relay control tube having a cathode, a control grid, and a plate, said relay control 'tube being operatively coupled to said sweep circuit, and a relay connected for energization by said relay control tube, the cathode of said relay control tube being maintained at a potential which is only a few volts less positive than the plate supply for the sweep circuit tube, the control grid of the relay control tube being maintained at the same potential as the plate of the sweep circuit tube, and the cathode of the sweep circuit tube being maintained at a negative potential relative to the potential of the cathode of the relay control tube which is substantially equal to the normal oper-- ating potential of the sweep circuit tube.

3. An electrical control system of the class de scribed comprising an oscillator, means which is responsive to the condition to 'be controlled to eiect a change in the frequency of the output of said oscillator, a rst relay means, a tuned circuit connected intermediate said first relay and said oscillator whereby the operation of said first relay is made dependent upon the frequency oi said oscillator, and means under the control of said first relay which is operable to eiiect the repetitive energizaticn of a second relay for very short intervals of time, said last mentioned means including a vacuum tube, saw-tooth sweep circuit, and a relay control tube having a, cathode, a plate, and a control grid co-upled to said sweep circuit, said relay control tube controlling the operation of said second relay, the cathode of said relay control tube -being maintained at a voltage which is only slightly less positive than the plate supply for the sweep circuit tube, the control grid of the relay control tube being maintained at the same potential as the plate of the sweep circuit tube, and `the cathode of the sweep circuit tube being maintained at a substantial negative potential relative to the potential of the cathode of the relay control tube..

4. An electrical control system of the class described comprising an oscillator, means including a float which is responsive to the density or level of the liquid condition which is to be controlled to eiect a change in the frequency of the output of said oscillator, a rst relay means, a tuned circuit connected intermediate said relay and said oscillator whereby the operation of said iirst relay is made dependent upon changes in the frequency of said oscillator, and means under the control of said iirst relay which is operable to effect the repetitive energization of a second relay for very short intervals of time, said last mentioned means including a gas lled triode connected in a sawtooth sweep circuit and a relay control tube having a cathode, a control grid, and a plate coupled to said sweep circuit, said relay control tube controlling the operation of said second relay, the cathode of said relay control tube being maintained at a potential which is only a few volts less positive than the plate supply for the sweep circuit tube, the control grid of the relay control tube being maintained at the same potential as the plate of the sweep circuit tube, and the cathode of the sweep circuit tube being maintained at 10 a negative potential relative to the potential of the cathode of the relay control tube which is substantially equal to the normal operating potential of the sweep circuit tube.

5. A control device comprising, in combination, means to generate a current responsive to the condition to be controlled, a normally closed relay connected to said generating means, a sawtoothed sweep circuit including a thyratron tube having a plate, grid, and cathode, the plate and grid of said thyratron tube being connected to the relay, a relay tube having a control grid connected to the plate of the thyra-tron, said tube being biased to conduct only during firing of the thyratron tube, and a second relay having a eld coil connected in series with the plate circuit of the relay tube.

6. A control device comprising, in combination, switching means adapted to be actuated by changes in the condition to be controlled, a sawtoothed generator connected to said switching means, said switching means interrupting the oscillation of the saw-toothed generator under normal unactuated conditions, a relay tube conf nected to the saw-toothed generator and biased to conduct only during periods of oscillation of the saw-toothed generator, said relay circuit being provided with arelay, whereby the relay may be used to control the actuating conditions.

REMSEN T. SCHENCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,228,163 Cohen Jan. 7, 1941 2,386,942 Edelman Oct. 16, 1945 2,433,599 Cohen Dec. 30, 194'? 2,442,238 Haungs May 25, 1948 2,488,505 Wannamaker Nov. 15, 1949 2,511,409 Mayberry June 13, 1950 

